rust: debugfs: use "kernel vertical" style for imports

rust: debugfs: use "kernel vertical" style for imports

Convert all imports in the debugfs Rust module to use "kernel vertical"
style.

With this subsequent patches neither introduce unrelated changes nor
leave an inconsistent import pattern.

While at it, drop unnecessary imports covered by prelude::*.

Link: https://docs.kernel.org/rust/coding-guidelines.html#imports
Acked-by: Greg Kroah-Hartman <gregkh@linuxfoundation.org>
Link: https://patch.msgid.link/20251218165626.450264-1-dakr@kernel.org
[ Apply the same change to the debugfs sample code. - Danilo ]
Signed-off-by: Danilo Krummrich <dakr@kernel.org>